libopus 1.2.1

Jun 26, 2017

This Opus 1.2.1 minor release fixes a relatively rare
issue where the 1.2 encoder would wrongly assume a signal to be bandlimited to 12 kHz and not encode frequencies
between 12 and 20 kHz. This only happens on a few clips, but it is good to update to avoid a potential
loss of quality.

There are no other changes compared to 1.2. Please report any problems.